Northern Brook Lamprey
All lampreys have snakelike bodies and smooth, slippery skin, lack a lower jaw, and have a mouth that consists of a rounded sucking disk. There are no paired fins. There are 7 pore-like gill openings along each side of the head. Unlike parasitic lampreys, brook lampreys as a group don’t have many teeth in their sucking disk, and the teeth they have are poorly developed, especially near the outer edge of the disk. When expanded, the sucking disk is narrower than the head. The northern brook lamprey has an undivided though shallowly notched dorsal fin, and all the disk teeth are poorly developed. In the innermost circle, all teeth are 1-pointed. Adults ready to spawn are darkish brown, becoming nearly black by the time spawning is completed. The larvae (ammocoetes) of all lampreys resemble the adults but lack eyes, and the mouth is a horseshoe-shaped hood instead of a sucking disk. Larvae and new adults are grayish brown above, yellow on the belly and fins.